Application Of Radiosurgery Research Articles

A simple plan strategy to optimize the biological effective dose delivered in robotic radiosurgery of vestibular schwannomas.

Using the concept of biologically effective dose (BED), the effect of sublethal DNA damage repair (SLR) on the bio-efficacy of prolonged radiotherapy treatments can be quantified (BEDSLR). Such treatments, lasting more than 20 min, are typically encountered in stereotactic radiosurgery (SRS) applications using the CyberKnife (CK) and Gamma knife systems. Evaluating the plan data from 45 Vestibular Schwannoma (VS) cases treated with single fraction CK-SRS, this work demonstrates a statistically significant correlation between the marginal BEDSLR delivered to the target (m-BEDSLR) and the ratio of the mean collimator size weighted by the fraction of total beams delivered with each collimator ((_w^m)Cs), to the tumor volume (Tv). The correlation between m-BEDSLR and (_w^m)Cs/Tv datasets was mathematically expressed by the power function m-BEDSLR= 85.21(±1.7%)∙((_w^m)Cs/Tv)^((0.05±7%) ) enabling continuous m-BEDSLRpredictions. Using this formula, a specific range of m-BEDSLRlevels can a priori be targeted during treatment planning through proper selection of collimator size(s) for a given tumor volume. Inversely, for a selected set of collimators, the optimization range of m-BEDSLRcan be determined assuming that all beams are delivered with the smallest and largest collimator size. For single collimator cases or when the relative usage of each collimator size is known or estimated, a specific m-BEDSLRlevel can be predicted within 3% uncertainty. The proposed equation is valid for the fixed CK collimators and a physical dose prescription (Dpr) of 13 Gy. For alternate Dpr in the range of 11 - 14 Gy, a linear relationship was found between relative changes of m-BEDSLR(Dpr) and Dpr with respect to m-BEDSLR(13Gy) and 13 Gy, respectively. The proposed methodology is simple and easy to implement in the clinical setting allowing for optimization of the treatment's bio-effectiveness, in terms of the delivered BED, during treatment planning.

Radiosurgery for Facial Pain: A Narrative Review.

The surgical treatment of pain has been an integral part of neurosurgery since the early 20th century when Harvey Cushing pioneered ganglionectomy for trigeminal neuralgia. Over the ensuing years, as anatomic and physiologic knowledge of pain systems grew, new techniques aimed at new targets were developed for various pain conditions. Our objective was to provide an informative and up-to-date summary of radiosurgery for chronic facial pain, emphasizing trigeminal neuralgia and discussing the advantages and challenges of this modality. A PubMed search with keywords ("trigeminal neuralgia" or "cluster headache" or "glossopharyngeal neuralgia") and ("radiosurgery") and ("systematic review" or "review") was conducted. Relevant publications in English published from January 2000 to May 2022 were screened manually for their title, abstract, and even full text to determine their relevance. References from the searched articles were also searched as other supplementary articles. We excluded original articles and personal series from the analysis and only considered systematic reviews to maintain the transparency in the record. A total of 19 studies for trigeminal neuralgia (n > 100), 52 cases of cluster headache, and 42 cases of glossopharyngeal neuralgia were found. Radiosurgery remains the safest among various treatment options with equitable pain control with other percutaneous procedures. MVD remains the gold standard for long-term pain control. There is no difference in efficacy or tolerance between patients treated with gamma knife, linear accelerator, or CyberKnife. The minimum recommended prescription dose was 70 Gy (level of evidence II), and the maximum dose was 90 Gy (level of evidence III) in a single fraction. Radiosurgery provides 5-year pain control in 50% of patients without medication (85% of patients with/without medication) with an average latency period of 1-3 months. Approximately 8-15% of patients will experience a recurrence of pain after an average period of 1 year. Prospective pain relief will be about 60% at 3 years, 40% at 7 years, and 37% in 10 years. The main complication was facial hypoesthesia occurring in 25-50% of patients within 6 months-3 years and disabling in 10% of cases. Cluster headache and glossopharyngeal neuralgia are emerging conditions for treatment with GKRS, although long-term efficacy remains to be studied. Having searched PubMed and other databases and summarized the application of radiosurgery for facial pain, we concluded that radiosurgery is undoubtedly a promising tool for chronic facial pain, but further studies are needed to realize its long-term efficiency and advanced applications of the same.

Effect of modulation factor and low dose threshold level on gamma pass rates of single isocenter multi-target SRT treatment plans.

SRS MapCHECK (SMC) is a commercially available patient-specific quality assurance (PSQA) tool for stereotactic radiosurgery (SRS) applications. This study investigates the effects of degree of modulation, location off-axis, and low dose threshold (LDT) selection on gamma pass rates (GPRs) between SMC and treatment planning system, Analytical Anisotropic Algorithm (AAA), or Vancouver Island Monte Carlo (VMC++ algorithm) system calculated dose distributions. Volumetric-modulated arc therapy (VMAT) plans with modulation factors (MFs) ranging from 2.7 to 10.2 MU/cGy were delivered to SMC at isocenter and 6cm off-axis. SMC measured dose distributions were compared against AAA and VMC++ via gamma analysis (3%/1mm) with LDT of 10% to 80% using SNC Patient software. Comparing on-axis SMC dose against AAA and VMC++ with LDT of 10%, all AAA-calculated plans met the acceptance criteria of GPR≥90%, and only one VMC++ calculated plan was marginally outside the acceptance criteria with pass rate of 89.1%. Using LDT of 80% revealed decreasing GPR with increasing MF. For AAA, GPRs reduced from 100% at MF of 2.7 MU/cGy to 57% at MF of 10.2 MU/cGy, and for VMC++ calculated plans, the GPRs reduced from 89% to 60% in the same MF range. Comparison of SMC dose off-axis against AAA and VMC++ showed more pronounced reduction of GPR with increasing MF. For LDT of 10%, AAA GPRs reduced from 100% to 83% in the MF range of 2.7 to 9.8 MU/cGy, and VMC++ GPR reduced from 100% to 91% in the same range. With 80% LDT, GPRs dropped from 100% to 42% for both algorithms. MF, dose calculation algorithm, and LDT selections are vital in VMAT-based SRT PSQA. LDT of 80% enhances sensitivity of gamma analysis for detecting dose differences compared to 10% LDT. To achieve better agreement between calculated and SMC dose, it is recommended to limit the MF to 4.6 MU/cGy on-axis and 3.6 MU/cGy off-axis.

P18.08.B COMPARISON OF DOSE CALCULATION PLANNING SYSTEMS FOR RECCURENT MENENGIOMA TREATED WITH FRACTIONATED RE-IRRIDATION

Abstract PURPOSE Meningioma is among the most common tumors of the central nervous system, accounting for approximately one-third of all brain tumors. Surgery is mainstay treatment and Radiotherapy (RT) provides long-term control in many patients, however recurrences following RT may occur and the safety and efficacy of a second course of RT is not well defined, technical and planning features are yet to be clarified. In this study, we compared various treatment planning systems (TPS) used in RT in a patient who had progressed meningioma after three applications of Gammaknife radiosurgery (GK-SRS). Case Presentation: 55-year-old male patient was diagnosed with grade-1 meningioma of the sphenoid wing in 2014 and subtotal excision was performed, with no further treatment. Progression was detected in 2016, and 11 Gy single fraction GK-SRS was applied in two sessions (inferior and superior parts of the tumor was irradiated in separate GK-SRS applications with 2 months apart) to the recurrent lesion in the right spheno-orbital region in a GK center. Patient was well until June 2022 when progression was detected in the right infratemporal region. Another GK-SRS application of 11 Gy was performed to the patient at the same institute.In April 2023 progression of the tumor was detected, tumor was irresectable and patient referred to our department for fractionated radiotherapy. Recurrent tumor was originating from right sfenoid wing and extending to right infratemporal fossa. We obtained the radiation dose distributions from the previous GK-SRS plans. Due to dose limits on the right optic nerve due to previous radiation dose disturbution , the conventional fractionated radiotherapy was planned . The PTV dose was planned to be 45 Gy/25 fx. Eclipse and Brainlab systems were compared for treatment planning. Right optic nerve dose of EQD2 was already above the limits, thus conventional fractionation (45 Gyin 25 fractions) was prescribed. Two separate plans were generated using Varian-Eclipse and Brainlab-Elements TPS, and the dose distribution of those plans were compared. Plan optimization was performed in both planning systems to provide PTV D%95. While the PTV Dmax was 57.24 Gy in BrainLAB, it was 48.7 Gy in Eclipse. Dmax doses for Brainlab and Eclipse were: right optic nerve 10.11 Gy vs. 26.9 Gy, chiasm 6.68 Gy vs. 20.5 Gy respectively. In Eclipse plan optimization, the collimator and table angles were optimized manually, while in Brainlab planning system, they were automatically handled, therefore normal tissues can be better preserved with increase of hot spots inside the PTV. This situation is observed clearly in this case. CONCLUSION Using different table and collimator angles in plan optimization can yield better results in providing normal tissue dose tolerance, especially in the irradiation of central nervous system.

Causes of Death in Patients With Brain Metastases.

Advances in targeted therapies and wider application of stereotactic radiosurgery (SRS) have redefined outcomes of patients with brain metastases. Under modern treatment paradigms, there remains limited characterization of which aspects of disease drive demise and in what frequencies. This study aims to characterize the primary causes of terminal decline and evaluate differences in underlying intracranial tumor dynamics in patients with metastatic brain cancer. These fundamental details may help guide management, patient counseling, and research priorities. Using NYUMets-Brain-the largest, longitudinal, real-world, open data set of patients with brain metastases-patients treated at New York University Langone Health between 2012 and 2021 with SRS were evaluated. A review of electronic health records allowed for the determination of a primary cause of death in patients who died during the study period. Causes were classified in mutually exclusive, but collectively exhaustive, categories. Multilevel models evaluated for differences in dynamics of intracranial tumors, including changes in volume and number. Of 439 patients with end-of-life data, 73.1% died secondary to systemic disease, 10.3% died secondary to central nervous system (CNS) disease, and 16.6% died because of other causes. CNS deaths were driven by acute increases in intracranial pressure (11%), development of focal neurological deficits (18%), treatment-resistant seizures (11%), and global decline driven by increased intracranial tumor burden (60%). Rate of influx of new intracranial tumors was almost twice as high in patients who died compared with those who survived ( P < .001), but there was no difference in rates of volume change per intracranial tumor ( P = .95). Most patients with brain metastases die secondary to systemic disease progression. For patients who die because of neurological disease, tumor dynamics and cause of death mechanisms indicate that the primary driver of decline for many may be unchecked systemic disease with unrelenting spread of new tumors to the CNS rather than failure of local growth control.

Radiosurgical treatment of solitary brain metastases using virtual cones with a standard multileaf collimator.

The virtual cone has been previously introduced as a novel technique for generating small, spherical dose distributions using a high-definition multileaf collimator (MLC) for functional radiosurgery applications. There has been no reported investigation into adapting this technique to a standard MLC for the treatment of solitary intracranial metastases as an alternative to physical stereotactic cones. This study characterizes the virtual cone technique adapted to a standard 5mmleaf-width MLC (VCSD ). VCSD dose distributions using MLC leaf gaps of 2-5mmwere generated and isodose sphericity metrics, peak dose gradients, optimal normalization ranges, and achievable field widths were compared to those of 5.0-12.5mmdiameter physical cones. Target sizes feasible to treat were identified and planned for comparison against established techniques using Paddick conformity index (PCI) and dose volume metrics. End-to-end validation of the VCSD technique was performed. VCSD and physical cones sphericity metrics agree within 3.5% and VCSD plans achieved a dose gradient of 21.3%mm-1 , comparable to 10.0-12.5mmdiameter physical cones. Normalization within the 50%-77% range preserves the optimal dose gradient within 2%⋅mm-1 and enables the treatment of 5-11mmdiameter planning target volumes (PTVs). Mean PCI for virtual and physical cones was 0.957 and 0.949, which compared favorably against conformal arc and VMAT (0.899 and 0.926). VCSD outperformed conformal arc and VMAT for all dose volume metrics, and the mean 50% dose volume differed from physical cones by<0.5cc for PTVs as small as 5mm.Validationmeasurementsshowed100% of points passing a 2% / 0.5mmgamma test for all plans. The VCSD technique efficiently generates spherical dose distributions for the treatment of small brain metastases. Characteristics of the VCSD dose distributions are sufficiently comparable to those of physical cones to support VCSD as an alternative for the treatment of spherical PTVs as small as 5mmin diameter.

Spatial distribution of the imaging dose and characterization of the scatter radiation contribution in CyberKnife radiosurgery

PurposeThe imaging dose for intra- and extra-cranial CyberKnife radiosurgery applications was calculated and the scattered radiation reaching the digital detectors was quantified and analyzed with regard to its origin. MethodsThe image guidance subsystem of the CyberKnife was modeled based on vendor-provided information. The emitted X-ray energy spectrum for 120 kV was estimated using the SpekPy software tool. Monte Carlo (MC) image acquisition simulations were performed to calculate the total, primary and scattered photon fluences reaching each detector as a function of the imaged object dimensions. MC calculations of the imaging dose were performed for intra- and extra-cranial applications assuming 120 kV and 10 mAs acquisition settings. ResultsThe amount of scattered radiation reaching each detector was found to depend on the dimensions of the imaged anatomical region, contributing more than 40 % to the total photon fluence for regions more than 20 cm thick. More than 20 % of this scattered radiation originates from the contralateral imaging field. A maximum organ dose of 1.5 mGy at the nasal bones and an average dose of 0.37 mGy to the eye lenses per image pair acquisition was calculated for head applications. An entrance imaging dose of 0.4 mGy was calculated for extracranial applications. ConclusionsScattered radiation reaching each detector in the skull and spine tracking applications can be reduced by acquiring the pair of radiographs sequentially instead of simultaneously. A dose of 3.7 cGy to the eye lenses is estimated assuming 100 image pair exposures required for treatment completion.

On the effect of dose delivery temporal domain on the biological effectiveness of central nervous system CyberKnife radiosurgery applications: theoretical assessment using the concept of biologically effective dose

Objective: The diversity in technical configuration between clinically available radiosurgery systems, results in accordingly diverse treatment times for the same physical dose prescription, spanning from several min to more than 1 h. This, combined with evidence supporting the impact of dose delivery temporal pattern on the bio-effectiveness of low-LET radiation treatments, challenges the ‘acute exposure’ assumption adopted clinically to estimate the biological outcome of a given treatment scheme under the concept of biologically effective dose (BED). Approach: In this work, the treatment plans of 30 patients underwent CyberKnife radiosurgery for vestibular schwannoma (VS), prescribing a marginal dose of 13 Gy to the tumor, were retrospectively reviewed and the corresponding dose distributions were resolved in the temporal domain. For this purpose, the dose delivery timeline for each treatment was calculated based on relevant treatment plan data and technical specifications of the CyberKnife system, while dosimetry data were independently acquired on a CT-based digital model of each patient using an in-house developed dose calculation algorithm. Main results: Results showed that CyberKnife delivers highly inhomogeneous dose rate distributions in the temporo-spatial domain. This influences the delivered BED levels due to alterations in the sublethal damage repair (SLR) occurring within the treatment session. Using a BED framework involving SLR effects, it was shown that each physical dose iso-surface is associated with a BEDslr range. For the patient cohort studied, a typical range of 2%, with respect to the mean BEDslr value was found at 1σ. Significance: The marginal BEDslr delivered to the tumor by the prescription dose iso-surface deteriorates with treatment time, involving both beam-on time and beam-off gaps. For treatment time, T, between 21 and 50 min, this can be expressed by Compared to the acute exposure approach, a BED ‘loss’ of 21% is associated with the delivery of 13 Gy to the VS-tumor in 35 min.

Image-Guided Stereotactic Radiosurgery for the Treatment of Spasticity and Pain: A Preliminary Experience.

BackgroundSpasticity is a major health problem worldwide. Response to current medical and rehabilitation treatments is often poor. Surgical treatment is available only for a very limited number of patients.AimWe recently reported the application of stereotactic radiosurgery as a treatment option for spasticity and related pain. This paper describes a larger experience using image-guided stereotactic radiosurgery targeting the cervical or lumbar spinal roots to relieve spasticity and pain in four patients.MethodsAll the patients had refractory spasticity and related pain, one patient had additional paroxystic neuralgic pain. The cause of spasticity and pain was a traumatic brain and/or spinal cord injury, brain and/or spinal cord surgery, and stroke. Symptoms affected the right superior limb in one patient, and the inferior limbs in three patients (unilaterally in two, bilaterally in one). According to the symptoms, one patient was treated at the cervical level (C7 right sensory root) and three patients at lumbar level (right L4, left S1, and L2 roots bilaterally). The target was selected on constructive interference in steady-state (CISS) MR, focusing the irradiation on the postganglionic sensory segment of the cervical root or the intra-foraminal dorsolateral sensory portion of the lumbar roots. Appropriate spasticity and pain scales were used to assess the patient’s status after the treatment.ResultsThe treatments were tolerated well. Marked symptomatic relief was found in all the treated patients. Improvements in spasticity and pain scales were observed up to the latest follow-up. After 2 years, the mean reduction of the visual analog scale (VAS) and Modified Ashworth Scale (MAS) was 64.3% and 43.7%, respectively, while the median reduction of MAS score was 50%.ConclusionsExcept for a previous case report, this is the first study describing a novel noninvasive technique based on image-guided radiosurgery to treat severe spasticity and pain due to brain and spinal cord injury. This novel technique appears to be safe and effective and deserves to be studied further.

Is gamma knife radiosurgery for skull base meningiomas with carotid artery encasement supported by efficacy and safety outcomes?

AbstractClinical outcomes were reviewed in 30 patients treated by gamma knife radiosurgery for skull base meningiomas with carotid artery encasement (SKBM‐CAE). The overall clinical improvement rate after treatment was 46%. At a median imaging follow‐up of 49 months, tumor volumes were unchanged, were larger, and were smaller or had resolved in 70%, 23%, and 7% of cases, respectively. The crude survival rate at 10 years was 20% and the complication (new cranial nerve deficit not accompanied by imaging‐shown tumor growth) rate was 10%. SKBM‐CAE is amenable to being effectively and safely controlled with the application of gamma knife radiosurgery.

Utility of machine learning algorithms in degenerative cervical and lumbar spine disease: a systematic review

Machine learning is a rapidly evolving field that offers physicians an innovative and comprehensive mechanism to examine various aspects of patient data. Cervical and lumbar degenerative spine disorders are commonly age-related disease processes that can utilize machine learning to improve patient outcomes with careful patient selection and intervention. The aim of this study is to examine the current applications of machine learning in cervical and lumbar degenerative spine disease. A systematic review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A search of PubMed, Embase, Medline, and Cochrane was conducted through May 31st, 2020, using the following terms: "artificial intelligence" OR "machine learning" AND "neurosurgery" AND "spine." Studies were included if original research on machine learning was utilized in patient care for degenerative spine disease, including radiographic machine learning applications. Studies focusing on robotic applications in neurosurgery, navigation, or stereotactic radiosurgery were excluded. The literature search identified 296 papers, with 35 articles meeting inclusion criteria. There were nine studies involving cervical degenerative spine disease and 26 studies on lumbar degenerative spine disease. The majority of studies for both cervical and lumbar spines utilized machine learning for the prediction of postoperative outcomes, with 5 (55.6%) and 15 (61.5%) studies, respectively. Machine learning applications focusing on degenerative lumbar spine greatly outnumber the current volume of cervical spine studies. The current research in lumbar spine also demonstrates more advanced clinical applications of radiographic, diagnostic, and predictive machine learning models.

Additive Fabrication of a Vascular 3D Phantom for Stereotactic Radiosurgery of Arteriovenous Malformations.

In this study, an efficient methodology for manufacturing a realistic three-dimensional (3D) cerebrovascular phantom resembling a brain arteriovenous malformation (AVM) for applications in stereotactic radiosurgery is presented. The AVM vascular structure was 3D reconstructed from brain computed tomography (CT) data acquired from a patient. For the phantom fabrication, stereolithography was used to produce the AVM model and combined with silicone casting to mimic the brain parenchyma surrounding the vascular structure. This model was made with tissues-equivalent materials for radiology. The hollow vascular system of the phantom was filled with a contrast agent usually employed on patients for CT scans. The radiological response of the phantom was tested and compared with the one of the clinical case. The constructed model demonstrated to be a very accurate physical representation of the AVM and its vasculature and good morphological consistency was observed between the model and the patient-specific source anatomy. These results suggest that the proposed method has potential to be used to fabricate patient-specific phantoms for neurovascular radiosurgery applications and medical research.

Investigating the impacts of intrafraction motion on dosimetric outcomes when treating small targets with virtual cones.

PurposeIntrafraction patient motion is a well‐documented phenomenon in radiation therapy. In stereotactic radiosurgery applications in which target sizes can be very small and dose gradients very steep, patient motion can significantly impact the magnitude and positional accuracy of the delivered dose. This work investigates the impact of intrafraction motion on dose metrics for small targets when treated with a virtual cone.Materials and MethodsMonte Carlo simulations were performed to calculate dose kernels for treatment apertures ranging from 1 × 2.5 mm2 to 10 × 10 mm2. The phantom was an 8.2‐cm diameter sphere and isotropic voxels had lengths of 0.25 mm. Simulated treatments consisted of 3 arcs: 1 axial arc (360° gantry rotation, couch angle 0°) and 2 oblique arcs (180° gantry rotation, couch angle ±45°). Dose distributions were calculated via superposition of the rotated kernels. Two different collimator orientations were considered to create a virtual cone: (a) each treatment arc was delivered twice, once each with a static collimator angle of ±45°, and (b) each treatment arc was delivered once, with dynamic collimator rotation throughout the arc. Two different intrafraction motion patterns were considered: (a) constant linear motion and (b) sudden, persistent motion. The impact of motion on dose distributions for target sizes ranging from 1 to 10 mm diameter spheres was quantified as a function of the aperture size used to treat the lesions.ResultsThe impact of motion on both the target and the surrounding tissue was a function of both aperture shape and target size. When a 0.5‐mm linear drift along each dimension occurred during treatment, targets ≥5 mm saw less than a 10% decrease in coverage by the prescription dose. Smaller apertures accrued larger penalties with respect to dosimetric hotspots seen in the tissues surrounding the target volume during intrafraction motion. For example, treating a 4‐mm‐sized target that undergoes 2.60 mm (3D vector) of continuous linear motion, the D5 in the concentric shells that extend 1, 2, and 3 mm from the surface of the target was 39%, 24%, and 14% smaller, respectively when comparing the delivery of a larger aperture (6 × 10 mm2) to a smaller aperture (2 × 5 mm2). Using a static collimator for shaping a virtual cone during treatment minimized the dosimetric impact of motion in the majority of cases. For example, the volume that is covered by 70% or more of the prescription dose is smaller in 60.4% of cases when using the static collimator. The volume covered by 50, and 30% or more of the prescription dose is also smaller when treating with a static collimator, but the clinical significance of this finding is unknown.ConclusionsIn this work, the dosimetric trade‐offs between aperture size and target size when irradiating with virtual cones has been demonstrated. These findings provide information about the tradeoffs between target coverage and normal tissue sparing that may help inform clinical decision making when treating smaller targets with virtual cones.

Progress and prospects of flattening filter free beam technology in radiosurgery and stereotactic body radiotherapy.

The aim of this work is to summarize and evaluate the current status of knowledge on flattening filter free (FFF) beams and their applications in stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). A PubMed search was undertaken in order to identify relevant publications using FFF and stereotactic radiotherapy as keywords. On a clinical aspect, lung tumors treated with FFF SBRT show promising results in terms of local control and overall survival with acute toxicities consistent with those that occur with standard radiotherapy. Beside lung, SBRT is suitable for different anatomical sites such as liver, prostate, cervix, etc. offering similar results: reduced treatment time, good tumor control and mild acute toxicities. Regarding brain tumors, the employment of SRS with FFF beams significantly reduces treatment time and provides notable normal tissue sparing due to the sharp dose fall-off outside the tumor.

Possible Overcoming of Tumor Hypoxia with Adaptive Hypofractionated Radiosurgery of Large Brain Metastases: A Biological Modeling Study.

The present biological modeling study evaluated possible application of adaptive hypofractionated stereotactic radiosurgery (HSRS), which involves escalation of the prescription dose according to the gradual decrease in the tumor volume between treatment sessions separated by 2- to 3-week intervals, in the management of large brain metastases. To investigate the effects of dose escalation during three-stage adaptive HSRS, a generalized biologically effective dose (gBED) model was applied. Accounting for both a nonuniform dose distribution inside the target and tumor hypoxia was implemented, and normal brain radiation dose distributions were assessed. In comparison with conventional three-stage HSRS (with an identical prescription dose of 10 Gy at each treatment session), adaptive HSRS resulted in a 30-40% increase in gBED. This effect was especially prominent in late-responding targets (with α/βratios from 3 to 10Gy) and in neoplasms containing a high percentage of hypoxic cells. Despite dose escalation in the target, irradiation of the adjacent normal brain tissue was kept within safe limits at a level similar to that applied in conventional three-stage HSRS. Adaptive HSRS theoretically results in significant enhancement of gBED in the target and may possibly overcome resistance to irradiation, which is caused by tumor hypoxia. These advantages may translate into higher treatment efficacy in cases of large brain metastases.

Bibliometric analysis of the top-100 most cited articles on the radiosurgical management of cerebral arteriovenous malformation

Background: Radiosurgery is an effective, alternative treatment modality in managing patients with cerebral arteriovenous malformations (AVMs). The present study aims to highlight the scholarly impact of the top-100 most cited articles on the radiosurgical management of AVMs.Methods: A title-specific search using the keyword “arteriovenous malformation” was conducted in the Scopus database. The outcome of the search was rearranged based on the citations count. Articles were categorized into four entities; clinical, gamma knife radiosurgery, linear accelerator (LINAC) radiosurgery, and proton beam radiosurgery. The exclusion criteria were applied to spinal or non-intracranial AVM, conference papers, non-English articles predominantly discussing the endovascular or microsurgical management.Results: The top-100 articles on the radiosurgical management of AVM were published between 1972 and 2016. Approximately one-third of the publications were produced between 1995 and 2000. The average citations per year for all papers were seven. The most-studied entity was pertinent to the clinical application of gamma knife radiosurgery in AVM (68%). The United States was the most active country in studying the radiosurgical application in AVM. The Journal of Neurosurgery published approximately one-third of the most-cited articles in the list. The top-3 most contributing authors, publishing 80% of articles in the list, were Lunsford et al.Conclusion: The radiosurgical management of AVMs evolved significantly throughout the years. Identifications of the publication trends facilitate the acquisition of evidence-based articles for authors investigating various radiosurgical techniques in the treatment of AVMs.

Evaluation of patient-specific MR distortion correction schemes for improved target localization accuracy in SRS.

This work aims at promoting target localization accuracy in cranial stereotactic radiosurgery (SRS) applications by focusing on the correction of sequence-dependent (also patient induced) magnetic resonance (MR) distortions at the lesion locations. A phantom-based quality assurance (QA) methodology was developed and implemented for the evaluation of three distortion correction techniques. The same approach was also adapted to cranial MR images used for SRS treatment planning purposes in single or multiple brain metastases cases. A three-dimensional (3D)-printed head phantom was filled with a 3D polymer gel dosimeter. Following treatment planning and dose delivery, volumes of radiation-induced polymerization served as hypothetical lesions, offering adequate MR contrast with respect to the surrounding unirradiated areas. T1-weighted (T1w) MR imaging was performed at 1.5T using the clinical scanning protocol for SRS. Additional images were acquired to implement three distortion correction methods; the field mapping (FM), mean image (MI) and signal integration (SI) techniques. Reference lesion locations were calculated as the averaged centroid positions of each target identified in the forward and reverse read gradient polarity MRI scans. The same techniques and workflows were implemented for the correction of contrast-enhanced T1w MR images of 10 patients with a total of 27 brain metastases. All methods employed in the phantom study diminished spatial distortion. Median and maximum distortion magnitude decreased from 0.7mm (2.10ppm) and 0.8mm (2.36ppm), respectively, to <0.2mm (0.61ppm) at all target locations, using any of the three techniques. Image quality of the corrected images was acceptable, while contrast-to-noise ratio slightly increased. Results of the patient study were in accordance with the findings of the phantom study. Residual distortion in corrected patient images was found to be <0.3mm in the vast majority of targets. Overall, the MI approach appears to be the most efficient correction method from the three investigated. In cranial SRS applications, patient-specific distortion correction at the target location(s) is feasible and effective, despite the expense of longer imaging time since additional MRI scan(s) need to be performed. A phantom-based QA methodology was developed and presented to reassure efficient implementation of correction techniques for sequence-dependent spatial distortion.

Application of stereotactic radiosurgery and radiotherapy in the treatment of Itsenko — Cushing’s disease

Cushing’s disease is caused by a pituitary tumor which causes increased production of adrenocorticotropic hormone, leading to chronic hypersecretion of cortisol by the adrenal cortices. Endoscopic transnasal adenomectomy is the initial treatment of choice with the greatest efficiency for the treatment of the disease. However in the absence of remission or relapse of hypercortisolism after neurosurgical surgery, as well as in cases when surgical intervention cannot be carried due to medical contraindications to surgical intervention, radiation treatment is used as an alternative or adjoining therapy. In this literature review the efficiency of different radiation techniques (the conventional and the modern techniques), as well as possible complications of modern methods of radiosurgery and radiotherapy have been looked for.

Clinical outcomes of fractionated stereotactic radiosurgery in treating perioptic meningiomas and schwannomas: A single-institutional experience

Application of radiosurgery to the newly diagnosed or post-operative residual perioptic lesions has been proved to improve tumor control. However, risk of vision injury induced by radiosurgery may increase substantially if the radiation dose is too high or tumor is close to the optic apparatus. The purpose of this study was to evaluate the safety and the effectiveness of fractionated stereotactic radiosurgery (FSRS) for perioptic tumors. We retrospectively analyzed 60 consecutive patients with 53 meningiomas and 7 schwannomas treated with FSRS between October 2007 and February 2020. We administered a marginal dose of 6–7 Gy (mean 6.8 Gy) per fraction and delivered 3 fractions in 3 consecutive days. The median tumor volume was 6.31 cm3 (range 0.3–58.23 cm3). The mean minimum lesion-optic distance (MLOD) is 0.85 mm (range 0–3 mm). After mean follow-up period of 69.6 months (range 6.82–156.32 months; median 58.9 months), the tumor control rates at 1, 3, 5, 8 and 13 years were 98.3%, 93.4%, 90.60%, 88.4% and 88.4%, respectively. Four out of the 60 tumors (6.7%) experienced a transient volume increase after FSRS. None of the patients developed visual impairment related to radiation induced optic neuropathy (RION) after FSRS. In conclusion, FSRS offers an alternative treatment option in treating perioptic meningiomas and schwannomas with acceptable tumor control rates and good visual preservation in the present study.

A Novel Approach for Treatment of Uterine Fibroids: Stereotactic Radiosurgery as a Proposed Treatment Modality

Minimally invasive therapeutic interventions and the field of stereotactic radiosurgery have advanced enormously in recent years. We briefly review the field of stereotactic radiosurgery and propose its use as a novel treatment modality for benign gynecologic conditions such as uterine fibroids. Computerized searches of Medline and PubMed were conducted using the key words “stereotactic radiosurgery,” “CyberKnife®,” “uterine fibroids,” and “radiation therapy.” References from identified sources were manually searched to allow for a thorough review. Data from relevant sources was compiled to create this review article. Stereotactic techniques have not only significantly reshaped the field of neurosurgery from open to noninvasive treatment, but also has impacted the field of radiation oncology by improving precision and reducing radiation exposure of normal tissues. Stereotactic radiation has proven to be a safe and effective method for the treatment of both benign and malignant conditions. Over the past two decades, new technologies have expanded the application of stereotactic radiosurgery to include spinal, renal, cardiac, lung, liver, prostate, and gynecologic cancers, and very recently even for the treatment of some non-neoplastic conditions such as cardiac arrhythmias. With success in so many disciplines, it is proposed that stereotactic radiosurgery may be a promising tool for the treatment of benign gynecologic conditions. Additional clinical experience is needed to further define the safety and efficacy of this proposed new treatment paradigm.